1. Technical Field of the Invention
This invention relates to making a finned body of a high-ductility material.
More particularly, the invention relates to a method of making a finned body having a multiplicity of thin, closely spaced fins, such as a finned body having a fin density of at least one fin per millimeter, e.g. 1,5 or more fins per millimeter, and a fin height to thickness ratio of at least 5.
2. Prior Art
The invention also relates to a machine for making a finned body of this kind.
Such finned bodies find use in heat transfer structures, such as heat exchangers of the kind in which heat is transferred through the fins between a liquid or gaseous first fluid flowing in the passages defined and separated by the fins and a second fluid flowing through other passages in the finned body. The finned body often is generally cylindrical with the fins extending radially outwardly generally transversely to the axis of the body and may be made of aluminium or other light metal material of high heat conductivity.
In a known class of heat exchangers of this kind (see, for example, WO86/00395 or U.S. Pat. No. 4,923,003) the fins and the intervening gaps are dimensioned and designed such that the fluid flows in laminar fashion in the gaps or passages defined between the fins. In these heat exchangers the fins are very thin and very closely spaced: the fins may have a thickness of a few tenths of a millimeter, e.g. about 0.2 mm, and may be separated by a gap of approximately the same width, e.g. about 0.2 or 0.3 mm, and the height of the fins may be greater by one order of magnitude, e.g. about 3 mm.
As is readily appreciated, the forming of the fins on such heat exchanger bodies presents special problems, particularly where the finned body is made of a soft material, such as aluminium or some other light metal. For example, machining of such materials is often troublesome, because the material tends to stick to the machining tool and possesses poor chip breaking properties and because the surface finish tends to be poor. Moreover, because of the small fin thickness the fins easily deform or rupture under the influence of the forces to which they are subjected in the fin forming operation.